Aim: This study investigated the cytotoxic effect of glass ionomers and compomers on Balb/C 3T3 fibroblasts. Materials and Methods: The materials that were investigated were; one conventional glass ionomer (Ketac-Fill/ESPE) and one resin modified glass ionomer (Vitremer/3M), three compomers (F2000/3M; Glasiosite/Voco; Dyract AP/Densply), and one flowable compomer (Dyract Flow/Densply). Twenty discs (2x5mm) were prepared from each material and then divided in two groups of ten. The discs in the first group were used to evaluate the cytotoxicity of the materials in direct contact with Balb/C 3T3 fibroblasts. While extracts of the discs from the second group were prepared in culture medium and tested for any cytotoxic effects on Balb/C 3T3 fibroblasts. Cell activity was evaluated using the MTT assay, and the results presented as percentage of negative controls (Teflon discs). Results: In the first group, Dyract AP was the least cytotoxic material followed by Glasiosite, Dyract Flow, F2000, Vitremer and Ketac Fill. Overall, the glass ionomer materials (Vitremer and Ketac-Fill) were significantly more cytotoxic than the compomer materials (p<0.05). For the second group, the extract of Glasiosite exhibited the least cytotoxic effect followed by extracts of Dyract AP, F2000, Vitremer, Dyract Flow and Ketac-Fill. Glasiosite and Dyract AP were significantly less cytotoxic than all the other materials tested (p<0.05). In both groups the flowable compomer, Dyract Flow, was found to be more cytotoxic than Dyract AP (p<0.05). Conclusion: Glass ionomer materials were more cytotoxic than compomer materials. The flowable compomer Dyract Flow was found to be more cytotoxic than the conventional compomer Dyract AP.